Does anybody think it's a bad idea to add the CF front splitters on the bumper or change the spoiler on the trunk? BMW did lots of testing with this car in the wind tunnel, and I'm pretty sure these additions to the car are going to mess all that research up.

But I guess if you don't drive at high speeds these changes will have an insignificant effect on the performance of your car if any at all.

Most of the aero work on a car is composed of the underside (one of the largest factors that most people don't even know about), and the nose and form factor running up and over the car. The decklid probably gets very little airflow over it, so modifying it probably won't have much of an impact at all. That's why the GT cars have their wings so high off of the trunk, just to grab some air.

Most of the aero work on a car is composed of the underside (one of the largest factors that most people don't even know about), and the nose and form factor running up and over the car. The decklid probably gets very little airflow over it, so modifying it probably won't have much of an impact at all. That's why the GT cars have their wings so high off of the trunk, just to grab some air.

I haven't looked at the bottom of an M (as my car hasn't been built yet) but I would assume that BMW hasn't gone as crazy as Ferrari do in working the smoothe flow of air along the bottom. If that's the case, I'd think that the splitters might add a touch of downforce (and drag as pointed out above) without having any real negative impact on the designed airflow of the car. I'd be hesitant to put them on just because I know I'd clip them on something during the first week of ownership. (Or better yet, leave the car backed out a touch so they don't get damaged, and have some lady in a Suburban hit the car while she's talking on her phone, when she would have missed me by three inches with a stock car.) To be completely honest, I don't think you could do many aero mods that would have much of an impact below 100mph in terms of noticeable performance. Maybe you'd have slightly more drag, which costs you an extra gallon of gas after 100 fill-ups, but I think all that could be noticeable is some noise from the part. (That's easy to hear on side-mirrors, but unlikely from a part bolted, literally, the furthest distance from your ear possible, on a moving car.) Just turn the radio up a click.